As an example of the processes for producing a highly-purified polyphenol product, it is known to charge a tea extract solution into a chromatographic column and then obtain its fractionation by focusing on the finding that an advance elimination of impurities from the tea extract makes it possible to isolate and purify tea catechins into individual tea catechins such as ester catechins and free catechins (Patent Document 1).
Another known process is to filter a tea extract through an ultrafiltration membrane the molecular weight cutoff of which is from 6,000 to 100,000 (Patent Document 2). This process is, however, accompanied by a problem in that due to the use of a membrane of micropore size, the passing property is so bad that its processing time could extremely increase, even though improvements may be observed in clarity and catechin purity.
It is also known that tea-leaf catechins of low caffeine content can be obtained when a tea extract is filtered through a combination of a ceramic membrane, ultrafiltration membrane and reverse osmosis membrane (Patent Document 3). This process, too, has a problem in that due to the use of the ceramic membrane, the membrane is thick and is poor in passing property and processing time and further, its non-uniform pore size results in somewhat inferior clarity, although the ceramic membrane is good in durability and high-pressure operability.    [Patent Document 1] JP-A-07-70105    [Patent Document 2] JP-A-02-6499    [Patent Document 3] JP-A-06-116258